The lithium-sulfur couple has one of the highest theoretical energy densities, which is about 2500 Whr Kg.sup.-1. However, when lithium is immersed in a saturated solution of sulfur in tetrahydrofuran (THF) it undergoes corrosion at a rapid rate, due to the reduction of the sulfur. A corrosion rate in excess of 100 mA cm.sup.2 was measured and thus it is evident that this system cannot constitute a practical electrochemical cell. It was reported by Kock & Young, Electrochemical Society Fall Meeting, Atlanta, Ga. (1977) that lithium reacts with THF giving butanol and a mixture of aldehydes.
U.S. Pat. No. 3,532,543 1970 (D. A. Nole and V. Moss) claims a cell having a Li-anode, a solvent selected from ethylene carbonate, propylene carbonate, gamma butyrolactone and dimethoxyethane, or mixtures thereof, and a solute comprising a soluble lithium salt, said electrolyte being initially prepared by dispersing CS.sub.2 and finely divided lithium powder in the solvent of the electrolyte and permitting the resultant mixture to undergo reaction, and sulfur containing cathode. There are described cells in which the solvent is a mixture of ether and alkyl carbonate. These cells have an OCV of 2.8 V. This OCV is much higher than 2.4 V which is the theoretical OCV of the Li/S couple. In these cells the ethyl carbonates (or the gamma butyrolactone) serve as soluble cathodes, thus giving the higher OCV. In addition, we have found that the addition of propylene carbonate to Li/S cells having THF as solvent, markedly reduces the utilization of the sulfur (Example 18).
H. Lauck, U.S. Pat. No. 3,915,743, (1975), claims a cell with a lithium anode (or Ca,Mg Al) and a positive sulfur electrode and electrolyte comprising a conductive salt and an organic solvent which contains BF.sub.3 and alkyl carbonate and glycol ether. The OCV of these cells was 2.8-3.0, indicating the oxidation of lithium by the alkyl carbonate. The BF.sub.3 was "necessary to prevent the formation of polysulfides during discharge". H. Lauck, U.S. Pat. No. 3,907,591, (1975), claims a cell having a negative electrode formed of light metal and an electrolyte containing a conductive salt in organic solvent, a positive sulfur electrode formed of amorphous, insoluble sulfur having an additive of conductive material. In his examples he used bortrihalogenide which "prevents formation of polysulfides during the discharging process and considerably increases the current output". The main claim is very general and problematic. For example, the "light metals", Al, Mg, Ca are not practically dischargeable in many organic solvents such as alkyl carbonates, DMSO, DMSU, and lithium will completely disintegrate within a few days in a solution of LiAlCl.sub.4 in ethers.
Dey, U.S. Pat. No. 3,806,369 claims a cell with a light metal anode, sulfur cathode and cation exchange membrane which separates the anode and the cathode. The purpose of the membrane was "to inhibit the migration of polysulfides from the cathode to the anode".